Protein Constructs Designed for Targeting and Lysis of Cells

ABSTRACT

The invention relates to a protein construct, comprising (i) a targeting moiety that is capable of binding to a target cell, and (ii) an effector immunogenic moiety that is capable of triggering an existing, vaccine-induced or natural, immune response. The protein construct, that is preferably in the form of a heteromultimeric protein, is useful for redirecting an immune response that was pre-existing in a patient, toward an undesired target cell.

The present invention relates to a protein construct, useful for redirecting an existing immune response, toward an undesired target cell.

Natural immune response is not sufficient to destroy undesired cells such as tumoral cells. Many efforts have been made to target these cells, in order to obtain a better immune response or a direct cytotoxicity. In this purpose bi-functional molecules, optionally heteromultimeric bi-functional molecules, have been proposed. In this context immunotoxins have been designed, that contain targeting domains that direct the molecules to target cells of interest (e.g., effector T lymphocytes) and toxic domains that kill the target cells. U.S. Pat. No. 6,492,498 describes a fusion protein molecule containing a toxic domain, a targeting domain, and at least one heterologous coupling moiety. U.S. Pat. No. 6,492,498 further describes multimeric forms of this protein molecule.

However such approach is still not fully satisfying. Firstly, all target cells are not destroyed. Secondly, immunotoxins that do not reach the target may be toxic to other cells.

The inventors now propose a dramatically different approach. They take benefit of an existing immune response in the patient, to redirect it toward undesired target cells, thereby causing cell lysis. For that purpose, they chose to use immunogenic fragments, that trigger an immune response that is already existing in the patient. Thanks to a targeting moiety, the immune response is then redirected toward the target cell.

A subject of the invention is thus a protein construct, comprising (i) a targeting moiety that is capable of binding to a target cell, and (ii) an effector immunogenic moiety that is capable of triggering an existing, vaccine-induced or natural, immune response. Most preferably the immune response is antibody-induced. The protein construct can be in monomeric form, or, advantageously in a multimeric form.

A preferred multimeric protein comprises a multimerizing scaffold bearing (i) at least one targeting moiety that is capable of binding to a target cell, and (ii) at least two, preferably between six and eight, effector immunogenic moieties that are capable of triggering an existing, vaccine-induced or natural, immune response. In a most preferred embodiment, the scaffold comprises the C-terminal part of the alpha chain of C4BP and/or of the beta chain of C4BP, and the effector immunogenic moiety is fragment C of tetanus toxin.

The invention further provides a pharmaceutical composition comprising such protein constructs, in association with a pharmaceutically acceptable carrier. Another subject of the invention is the use of such protein constructs, for the preparation of a medicament intended for redirecting an immune response that was pre-existing in a patient, toward an undesired target cell, e.g. a tumor cell or an erythrocyte.

Advantageously the medicament causes destruction of said target cell. Complexes are formed between the protein constructs of the invention and target cells, leading to an activation of downstream biologic effector mechanisms, such as complement or Antibody Dependant Cell Cytotoxicity (ADCC), that result in the elimination of the target.

A particular subject of the invention is the use of a heteromultimeric protein comprising fragment C of tetanus toxin as an effector moiety, for the preparation of a medicament intended for redirecting an immune response in a patient who is naturally vaccinated against tetanus, or was previously subjected to a vaccination against tetanus. The anti-tetanus antibodies are recruited by the fragment C of tetanus toxin of the protein constructs, and can activate the complement system or cytotoxic cells, ultimately leading to the lysis of the target cell.

Targeting Moiety

The targeting moiety is a polypeptide that shows affinity for a target cell. Preferably it allows a specific binding to said target cell.

In a preferred embodiment, it is selected from the group consisting of an antibody, a binding fragment thereof, a ligand to a target cell receptor, and a lectin. As used herein, the term “binding fragments” of antibodies refers to antigen-binding fragments, e.g., Fab, F(ab′)₂, Fv, and single chain Fv fragments. Antibodies, or antibody fragments can be specific for (i.e., will have significant binding affinity for) a molecule expressed on the surface of a target cell of interest. Thus, they can have specific binding affinity for molecules such as T cell surface molecules (e.g., CD3 polypeptides, CD4, CD8, CD2, CD7, cytokine or growth factor receptors, or TCR), B cell surface molecules (e.g., CD19, CD20, CD22, cytokine or growth factor receptors, or Ig molecules), molecules expressed on tumor cells, and molecules expressed on the surface of infected target cells (e.g., viral proteins and glycoproteins).

More particularly, the targeting moiety may be an antibody, or a binding fragment thereof, against a tumor associated antigen, e.g. the carcinoembryonic antigen. Carcinoembryonic antigen (CEA) is a tumor marker which can be present on the membrane cells surface of various cancer such as pancreatic, gastric, colonic, ovarian and breast carcinoma. Other tumor associated antigens are, among others, oncofetal antigens, MART-1, Mage-1, Mage-3, gp 100, tyrosinase, CEA, her2/neu, PSA, CA-125, erb-2, Muc-1, Muc-2, point mutated ras oncogenes, point mutated p53 oncogenes, and TAG-72.

It may also be an antibody, or a binding fragment thereof, against a Rhesus antigen, especially Rhesus D antigen.

Antibodies against Glycophorin A are useful to target erythrocytes. Glycophorin A (GPA) is an abundant glycoprotein on the human erythrocyte membrane surface (0,3.106 to 1,2.106 site/erythrocyte). In the Examples presented herein, a recombinant anti-GPA scFv (30 kDa) was derived from a monoclonal IgG2b antibody (R18) which has a high affinity for the glycophorin A.

The targeting moiety can also be immunoglobulin (Ig) molecules of irrelevant specificity (or immunoglobulin molecule fragments that include or contain only an Fc portion) that can bind to an Fc receptor (FcR) on the surface of a target cell (e.g., a tumor cell).

The targeting moiety can further be cytokines, TNF-alpha, vascular endothelial growth factor (VEGF), and epidermal growth factor (EGF) colony stimulating factors (e.g., GM-CSF), hormones (e.g., insulin, or growth hormone), ligands for signal transduction receptors (e.g., CD40 ligand, an MHC class I molecule or fragments of an MHC molecule involved in binding to CD8, an MHC class II molecule or the fragment of an MHC class II molecule involved in binding to CD4), or ligands for adhesion receptors, e.g., ICAM-1, ICAM-2, or fibronectin or a domain (e.g., one containing one or more of the “Arg-Gly-Asp” repeats) of fibronectin involved in binding to integrin molecules. In addition a targeting domain could be Fas or Fas ligand or other death domain containing polypeptides (e.g., members of the TNF receptor family) or ligands for such polypeptides (e.g., TNF-alpha, or TWEAK).

Effector Moiety

The effector moiety refers to a polypeptide that activates an existing immune response. An existing immune response includes a natural immune response or the immune response induced by a vaccination against a pathogenic agent, e.g. a virus or a bacteria. The term “natural immune response” refers the immune response that has developed naturally in a patient. Such natural immune response includes the antibodies that have been produced by the body after an infection, or the antibodies of spontaneous existence, that recognize the cell elements, e.g. anti-actine antibodies or other natural antibodies of weak affinity and high connectivity.

Such effector moiety is not toxic by itself. It contains B cell epitope(s) and is capable of inducing an antibody response.

In a preferred embodiment, the effector moiety is a vaccine antigen, e.g. a toxin fragment that is immunogenic but non-toxic.

For example, it may be fragment C of tetanus toxin (TTFgC). Tetanus Toxin (TT) is a potent neurotoxin of molecular weight 150 KDa produced by the anaerobic bacterium Clostridium tetani. It consists of two polypeptide chains connected through an interchain disulfide bound. The larger fragment or heavy chain (100 KDa) contains the toxin's binding and translocation domain. The smaller polypeptide or light chain (50 KDa) is a zinc-dependant protease which cleaves synaptobrevin 2, blocking exocytosis of inhibitory transmitters. The Tetanus Toxin Fragment C (TTFgC) which is the 50 KDa C-terminal portion of the heavy chain, retains the neuronal and protein-binding activity and the uptake properties of the holotoxin without the toxic activity. TTFgC has the advantage of being non-toxic and virtually devoid of any action on the nerve processes in which they are transported. TTFgC is a known immunogen protective against tetanus, which was used for cell-lysis.

Other examples of effector moiety include an anatoxic fragment of diphtheria toxin, or a surface antigen of a virus, such as Hepatitis B virus.

In another embodiment, the effector moiety can further be a self-antigen against which natural antibodies exist. Further examples of effector moiety thus include antigenic cytoskeleton proteins, e.g. actine or tubuline, or antigenic fragments thereof. Indeed, antibodies of the IgM, IgG and IgA classes, reactive with a variety of serum proteins, cell surface structures and intracellular structures, are ‘naturally’ found in all normal individuals. Present in human cord blood and in ‘antigen-free’ mice, their variable-region repertoire is selected by antigenic structures in the body and remains conserved throughout life. Encoded by germline genes with no, or few, mutations, natural autoantibodies are characteristically ‘multireactive’ and do not undergo affinity maturation in normal individuals. Natural autoantibodies participate in the equilibrium of the immune system, contributing to controlled production of antibodies, accelerated elimination of external antigens or aged autoantigens, and to triggering of a specific immune response. They may participate in a variety of physiological activities, from immune regulation, homeostasis and repertoire selection, to resistance to infections, transport and functional modulation of biologically active molecules (Coutinho A, Kazatchkine M D, Avrameas S. Curr Opin Immunol. 1995 December; 7(6):812-8; Ternynck T. Druet P. Avrameas S. Rev Prat. 1994 January 1; 44(1):36-8; Avrameas S. Ternynck T. Mol. Immunol. 1993 August; 30(12):1133-42).

The Protein Construct

The targeting moiety and the effector moiety can be linked by a variety of methods.

In a preferred embodiment, they may be linked by means of a multimerizing scaffold, and the protein construct then preferably is in the form of a heteromultimeric protein. In a more preferred embodiment, the scaffold is a C4BP protein, or comprises a multimerizing fragment thereof [Libyh et al, Blood. 1997, 90(10):3978-83, Oudin et al, 2000, Journal of Immunology, 164,1505, and WO97/04109].

More particularly, the scaffold comprises the C-terminal part of the alpha chain of C4BP and/or of the beta chain of C4BP.

The C4BP molecule is found in normal human plasma. It has a spider-like structure made of seven α-chains and one 1-chain but minor forms made from only seven α-chains or five α/1β-chain molecules have also been described. The basic repetitive structure of both chains is termed short consensus repeat (SCR). Each SCR of about 60 amino acids includes two intrachain disulfide bridges. The C-terminal part of the C4BP lacks biological function and is responsible for the polymerization of the molecule in the cytoplasm of C4BP producing cells. The C-terminal part of the α-chain of C4BP is preferred to set up homo and hetero multimers, due to these properties as well as to its nonimmunogenicity of a normal human plasma protein.

The heteromultimeric protein construct may preferably comprise at least one targeting moiety and at least 2, preferably at least 5 or 6 effector moieties. Such heteromultimeric protein construct can be prepared by various methods. In a particular embodiment it is prepared by a method comprising

a) transfecting host cells with a nucleic acid vector that encodes the targeting moiety fused to a first scaffold polypeptide, and with a nucleic acid vector that encodes the effector moiety fused to a second scaffold polypeptide, wherein said second scaffold polypeptide is capable of multimerization with said first scaffold polypeptide, b) expressing the expression products and allowing them to multimerize; c) recovering the heteromultimeric protein constructs thus produced.

More particularly the host cells can be co-transfected with said two nucleic acid vectors.

Alternatively the method can comprise

a1) transfecting a host cell with a nucleic acid vector that encodes the targeting moiety fused to a first scaffold polypeptide, under conditions allowing expression of said targeting moiety fused to said scaffold polypeptide; a2) transfecting another host cell with a nucleic acid vector that encodes the effector moiety fused to a second scaffold polypeptide, under conditions allowing expression of said targeting moiety fused to said scaffold polypeptide, wherein said second scaffold polypeptide is capable of multimerization with said first scaffold polypeptide, b) recovering the expression products and contacting them under conditions that allow them to multimerize.

In preferred embodiments, it is described two models of heterofunctional molecules that bind to cells and induce the complement-dependent cells lysis. Multimerizations of TTFgC with anti-GPA scFv or anti-CEA VHH were provided by the multimerizing potential of the complement binding protein (C4BP).

cDNA containing the C-terminal part of the C4BPα coding sequence was fused with the sequence coding for the protein of interest (TTFgC, anti-GPA scFv or anti-CEA) and C4BPβ coding sequence was fused with the anti-GPA scFv sequence coding and then transfected in eukaryotic or insect cells as a single-phase construct for in vitro protein expression. The chimera proteins spontaneously multimerize in the cytoplasm of transfected cells that secrete covalently linked multimeres. Cotransfection of cells by two different vectors containing sequences coding for two distinct multimeric molecules lead to the production of a heteromultimeric protein with valences from both molecules covalently linked together by disulfide bridges.

In a first model, a TTFgC-C4BPα/anti-GPA scFv-C4BPα heteromultimeric molecule was produced. In vitro this heteromultimeric protein was able to bind to the erythrocyte surface and to induce an erythrocyte complement-dependant lysis. A TTFgC-C4BPα/anti-GPA scFv-C4BPα heteromultimeric molecule was also produced. In vitro this heteromultimeric protein was able to bind to the erythrocyte surface. In a second model TTFgC-C4BPα/anti-CEA-C4BPα molecule was also produced. This heteromultimeric molecule allowed the redirection of existing TT vaccine induced immuno-response towards human colon carcinoma cells tumor cells by targeting and destruction of them.

In another embodiment, the protein construct is a monomer comprising a targeting moiety and an effector moiety. The targeting moiety and the effector moiety can be linked by any methods such as fusion or covalent binding. The present invention further provides nucleic acids that encode such monomer fusion proteins. Such nucleic acid may be useful for the preparation of a medicament intended for redirecting an immune response that was pre-existing in a patient, toward an undesired target cell.

The monomer fusion proteins of the invention can further be linked to each other by methods known in the art, to form multimeric proteins. For example, a terminal or internal cysteine residue on one monomer can be utilized to form a disulfide bond with a terminal or internal cysteine residue on another monomer. Monomers can also be cross-linked using any of a number of known chemical cross linkers. While these cross-linking methods can involve residues (“coupling moieties”) that are native to either of the domains of the monomers, they can also be used to cross-link non-native (“heterologous”) residues incorporated into the polypeptide chains. While not necessarily the case, such residues will generally be amino acids (e.g., cysteine, lysine, arginine, or any N-terminal amino acid). The coupling moieties are preferably at the termini (C or N) of the monomers. They can be, as indicated above, a cysteine residue on each monomer, or a cysteine on one and a lysine on the other. Where they are two cysteine residues, cross-linking can be effected by, for example, exposing the monomers to oxidizing conditions.

The multimeric proteins can contain two or more (e.g., three, four, five, six, seven or eight) of the monomeric proteins described above. Each monomer can be identical, i.e., contain the same targeting and effector moieties and have the same amino acid sequence. Alternatively, they can be different. Thus, they can contain, for example, the same targeting moieties but different effector moieties, different targeting moieties but the same effector moieties, or different targeting moieties and different effector moieties. Where different targeting moieties are used, they will generally have significant binding affinity for either the same cell-surface molecule or for different molecules on the surface of the same cell.

Therapeutic Applications

The protein construct of the invention is useful to target and kill undesired cells in vivo.

It is herein described a method of killing undesired cells in a patient, wherein said patient is administered with an effective amount of the protein construct of the invention.

Destruction of Rhesus D erythrocytes is of particular interest, as it is a source of foetus-mother incompatibility.

Other appropriate patients include, without limitation, transplant (e.g., bone marrow, heart, kidney, liver, pancreas, lung) recipients, those with any of a variety of tumors (e.g., hematological cancers such as leukemias and lymphomas, neurological tumors such as astrocytomas or glioblastomas, melanoma, breast cancer, lung cancer, head and neck cancer, gastrointestinal tumors, genitourinary tumors, and ovarian tumors, bone tumors, vascular tissue tumors), those with any of a variety of autoimmune diseases, or those with an infectious disease involving an intracellular microorganism (e.g., Mycobacterium tuberculosis, Salmonella, influenza virus, measles virus, hepatitis C virus, human immunodeficiency virus, and Plasmodium falciparum). In transplant recipients, the protein construct is delivered, for example, to T cells, thereby resulting in the death of a substantial number, if not all, of the T cells. Delivery of an appropriate protein construct to tumor cells can result in the death of a substantial number, if not all, of the tumor cells. In the case of infection, the protein construct is delivered to the infected cells, thereby resulting in the death of a substantial number of, in not all, the cells and thus a substantial decrease in the number of, if not total elimination of, the microorganisms. In autoimmune diseases, the protein construct can contain a targeting moiety directed at the T cells (CD4+ and/or CD8+) and/or B cells capable of producing antibodies that are involved in the tissue destructive immune responses of the diseases.

The effector moiety is selected according to the immune profile of the patient, i.e. according to the existing immune response the patient has developed, either naturally, or further to a vaccination.

For in vivo administration, the protein constructs are generally associated with a pharmaceutically-acceptable carrier (e.g., physiological saline) and administered orally or by intravenous infusion, or injected subcutaneously, intramuscularly, intraperitoneally, intrarectally, intravaginally, intranasally, intragastrically, intratracheally, or intrapulmonarily. They are preferably delivered directly to an appropriate tissue, e.g., lymphoid tissue such as spleen, lymph nodes, or gut-associated lymphoid tissue in which an immune response (as, for example, in GVHD or an autoimmune disease) is occurring. The dosage required depends on the choice of the route of administration, the nature of the formulation, and the patient. Suitable dosages are in the range of 0.01-100.0 μg/kg.

In another in vivo approach, an expression vector containing one or more coding sequences encoding one or more fusion proteins of the invention, each coding sequence being separately transcribed, can be delivered to an appropriate cell of the subject. Alternatively, more than one expression vector, each containing a coding sequence encoding a different fusion protein, can be delivered to the appropriate cell. As the latter process would require that each expression vector be incorporated into a cell of interest, the approach using a single vector containing one or more coding sequences will be more efficient. The fusion proteins are designed such that, after translation, the fusion proteins will be multimerized by normal physiological mechanisms within the cell. Thus, for example, the fusion proteins can be linked by the formation of inter-fusion protein disulfide bonds or by non-covalent hydrophobic interactions between two or more fusion proteins.

For example, expression can be directed to a transplanted tissue or cell. An appropriate expression vector can, for example, be delivered directly to a tumor or, at the time of surgery, to tissues in the region of the body of the subject from which the tumor was surgically removed. It is not required that expression of the fusion protein be directed to the target cell itself. Indeed, expression will preferably not be by the target cell alone since, in this case, killing of the target cells by the protein construct would result in the depletion of the source of the protein construct.

The below figures and examples illustrate the invention without limiting its scope.

FIGURES

FIG. 1 shows the map of the TTFgC-C4BPα construct for transfection in 293T cells.

FIG. 2 shows the map of the anti-GPA scFv-C4BPα construct for transfection in 293T cells.

FIG. 3 shows the map of the TTFgC-C4BPα construct for transfection in SF9 cells.

FIG. 4 shows the map of the anti-GPA scFv-C4BPα construct for transfection in SF9 cells.

FIG. 5. Direct hemagglutination of erythrocytes (E). Incubation of E with:

1. R18 antibody (positive control). 2. TTFgC-C4BPα construct transfected 293T cell supernatant 3. anti-GPA scFv-C4BPα construct transfected 293T cell supernatant 4. TTFgC-C4BPα and anti-GPA ScFv-C4BPα constructs transfected 293T cell supernatant

FIG. 6. Analysis of TTFgC-C4BPα/anti-GPA scFv-C4BPα and TTFgC-C4BPα anti-GPA scFv-C4BPβ binding on E by flow cytometry. E were incubated with:

a. TTFgC-C4BPα transfected cell supernatant. b. anti-GPA scFv-C4BPα transfected cell supernatant. c. Non-transfected cell supernatant. d. TTFgC-C4BPα/anti-GPA scFv-C4BPβ transfected cell supernatant. e. TTFgC-C4BPα/anti-GPA scFv-C4BPβ transfected cell supernatant. f. TTFgC-C4BPα/anti-GPA scFv-C4BPα transfected cell supernatant.

FIG. 7. TTFgC-C4BPα/anti-GPA scFv-C4BPα distribution pattern was analyzed using fluorescence microscopy.

FIG. 8. Analysis of TTFgC-C4BPα/anti-CEA VHH-C4BPα binding by flow cytometry. LS174T cell were incubated with:

a. TTFgC-C4BPα transfected cell supernatant. b. Multimeric anti-CEA VHH-C4BPα transfected cell supernatant. c. TTFgC-C4BPα/anti-CEA VHH-C4BPα transfected cell supernatant. d. Monomeric anti-CEA VHH-c-myc transfected cell supernatant as positive control

FIG. 9. Analysis of TTFgC-C4BPα/anti-CEA VHH-C4BPα distribution pattern using fluorescence microscopy.

FIG. 10. Analysis of cascade complement activation by TTFgC-C4BPα/anti-GPA scFv-C4BPα molecules, revealed by a biotinylated monoclonal anti-human C4d antibody.

Erythrocytes were Incubated with: a. TTFgC-C4BPα transfected cell supernatant and heat inactivated serum containing high level of anti-TTFgC. b. TTFgC-C4BPα transfected cell supernatant and C5-deficient serum. c. TTFgC-C4BPα/anti-GPA scFv-C4BPα cell supernatant and C5-deficient serum. d. TTFgC-C4BPα transfected cell supernatant

FIG. 11. Analysis of (A) C3b (revealed by fluorescein-labeled goat antiserum) and (B) C4d (revealed by anti-C4d biotinylated monoclonal anti-Human C4d antibody) distribution pattern by fluorescence microscopy.

FIG. 12. O.D (630-405 nm) corresponds to the absorbance of haemoglobin; which indicates the degree of erythrocyte lysis.

a. Erythrocytes lysed with repetitive cycles of freezing/defreezing (100% of erythrocyte lysis). b. Erythrocytes with TTFgC-C4BPα/anti-GPA scFv-C4BPα supernatant. c. Erythrocytes with TTFgC-C4BPα supernatant. d. Erythrocytes with anti-GPA scFv-C4BPα supernatant. e. Erythrocytes with non-transfected cell supernatant. f. TTFgC-C4BPα/anti-GPA scFv-C4BPα supernatant, without erythrocytes.

The minimal value of O.D (˜0.200) corresponded to the absorbance of the serum.

EXAMPLES Example 1 Targeting and Lysis of Cells Using Heteromultimeric Recombinant Proteins Materials and Methods

1 Cloning of Anti-GPA Heavy and Light Chain Variable Region Coding Sequences and Assembly into an scFv

The Single-chain Fv (scFv) was constructed according to the method described by Marks et al. Briefly, RNA was extracted from mouse hybridoma secreting the monoclonal anti-glycophorin antibody R18 (kindly provided by J. P CARTRON, Institut National de Transfusion Sanguine, Paris, France). cDNA was generated using the Mouse scFv Module kit (Amersham Pharmacia, Orsay, France), the V_(H) and V_(L) genes were amplified by PCR using primers specific for the variable region of each chain and, finally, assembled into a single gene using a linker DNA fragment which maintains the correct reading frame. The assembly reaction ultimately produced the scFv gene where the V_(H) region was linked to the V_(L) region through a sequence encoding a (Gly₄Ser)₃ peptide.

2 DNA Constructions and 293T Cell Transfections 2.1 Cloning of the TTFgC-C4BPα Construct

DNA encoding TTFgC was kindly provided by P. MUNRO (Unité INSERM U 452, Faculté de Médecine de Nice, France). PCR amplification of TTFgC DNA was achieved by forward primer: 5′-CGCGAGAGATCTCTGGATTGTTGGGTTGATAAT-3′ (SEQ ID NO:9) and reverse primer: 5′-CGCGAGTCCGGAATCATTTGTCCATCCTTCATC-3′ (SEQ ID NO:10). Restriction sites BgIII and BspEI (underlined sequences) were inserted into forward and reverse primers respectively to facilitate TTFgC subcloning. A 100 μl reaction mixture was prepared, containing 500 ng of DNA, 500 ng of 3′ and 5′ primers, 16 nM dNTP, 10 mM Tris-HCl (pH 8,3), 50 mM KCl, 1.5 mM MgCl₂ and 2 U of AmpliTaq DNA polymerase (Perkin-Elmer, Roissy, France), then subjected to 30 cycles of amplification [30 s at 94° C., 30 s at 42° C., 2 min at 72° C.] using a GenAmp PCR System 9600 (Perkin-Elmer). PCR products were analyzed by electrophoresis on a 2% agarose gel.

PCR amplification of C4BPα was fulfilled by forward primer: 5′-CGCGAGTCCGGAGGCGGTGGCTCGACCGGA-3′ (SEQ ID NO:11) (Eurogentec, Angers, France) and reverse primer: 5′-CGCGAGTCTAGATTATCAGTGATGGTGATGGTGATGGTGGTGGATTAGTTCT TTATC-3′ (SEQ ID NO:12) (Eurogentec, Angers, France). Restriction sites BspEI and XbaI (underlined sequences) were inserted into forward and reverse primers respectively to facilitate C4BPα subcloning. A 100 μl reaction mixture was prepared, containing 500 ng of DNA, 500 ng of 3′ and 5′ primers, 16 nM dNTP, 10 mM Tris-HCl (pH 8.3), 50 mM KCl, 1.5 mM MgCl₂ and 2 U of AmpliTaq DNA polymerase (Perkin-Elmer, Roissy, France), then subjected to 30 cycles of amplification [30 s at 94° C., 30 s at 60° C., 30 s at 72° C.] using a GenAmp PCR System 9600 (Perkin-Elmer).

The amplified products of 1371 bp for TTFgC and 225 bp for C4BP were purified by QIAquick PCR Purification Kit protocol (Qiagen, Hilden, Germany) and ligated in pEFIRES-P vector (kindly provided by X.DERVILLEZ, Institute for Biomedical Research Frankfurt, Germany) by T4 DNA ligase (Stratagene, Hwy, USA). The recombinant clones were screened on Luria-Bertani agar containing ampicillin 100 μg/ml. The clones were selected after BgIII and XbaI digestion of each plasmid DNA obtained by mini-lysate preparation. One clone was sequenced (Genomexpress, Meylan, France) to confirm the presence of the TTFgC-C4BPα insert and whether it was cloned in frame and was chosen for expression studies (FIG. 1, and sequences SEQ ID NO:1 and NO:2).

2.2 Cloning of the Anti-GPA scFv—C4BPα Construct

The assembled anti-GPA scFv DNA fragment was amplified using forward primer 5′-CGCGAGAGATCTCAGGTGAAACTGCAGCAG-3′ (SEQ ID NO:13) (Eurogentec, Angers, France) and reverse primer 5′-CGCGAGTCCGGACCGTTTTATTTCCAGCTT-3′ (SEQ ID NO:14) (Eurogentec, Angers, France). The restriction sites BgIII and BspEI (underlined sequences) were inserted into forward and reverse primers respectively to facilitate anti-GPA scFv subcloning. A 100 μl reaction mixture was prepared, containing 500 ng of DNA, 500 ng of 3′ and 5′ primers, 16 nM dNTP, 10 mM Tris-HCl (pH 8,3), 50 mM KCl 1.5 mM MgCl₂ and 2 U of AmpliTaq DNA polymerase (Perkin-Elmer, Roissy, France), then subjected to 30 cycles of amplification [30 s at 94° C., 45 s at 64° C., 1 min at 72° C.] using a GenAmp PCR System 9600 (Perkin-Elmer). PCR products were analyzed by electrophoresis on a 2% agarose gel. PCR amplification of C4BPα was done as previously described.

The amplified products of 770 bp for anti-GPA scFv and 225 bp for C4BPα were purified by QIAquick PCR Purification Kit protocol (Qiagen, Hilden, Germany) and ligated in pEFIRES-P vector. The ligation product was introduced into Escherichia coli and one positive clone was sequenced (Genomexpress, Meylan, France) (FIG. 2, and sequences SEQ ID NO:3 and NO:4).

2.3 Cloning of the Anti-GPA scFv —C4BP β Construct

The assembled anti-GPA scFv DNA fragment was amplified using forward primer 5′-CGCGAGAGATCTCAGGTGAAACTGCAGCAG-3′ (SEQ ID NO:13) (Eurogentec, Angers, France) and reverse primer 5′-CGCGAGGCGGCCGCCCGTTTTATTTCCAGCTTG-3′ (SEQ ID NO:15) (Eurogentec, Angers, France). The restriction sites BglII and NotI (underlined sequences) were inserted into forward and reverse primers respectively to facilitate Anti-GPA scFv subcloning. A 100 μl reaction mixture was prepared, containing 500 ng of DNA, 500 ng of 3′ and 5′ primers, 16 nM dNTP, 10 mM Tris-HCl (pH 8.3), 50 mM KCl 1.5 mM MgCl₂ and 2 U of AmpliTaq DNA polymerase (Perkin-Elmer, Roissy, France), then subjected to 30 cycles of amplification [30 s at 94° C., 45 s at 58° C., 1 min at 72° C.] using a GenAmp PCR System 9600 (Perkin-Elmer).

PCR amplification of C4BPβ was fulfilled by forward primer: 5′-CGCGAGGCGGCCGCATCCGGAGGCGGTGGCTCG-3′ (SEQ ID NO:16) (Eurogentec, Angers, France) and reverse primer: 5′-CGAGTCTAGATCAGTGATGGTGATGGTGATGGATCAACAATTTTGCCTTCAA-3′ (SEQ ID NO:17) (Eurogentec, Angers, France). Restriction sites NotI and XbaI (underlined sequences) were inserted into forward and reverse primers respectively to facilitate the C4 bpβ subcloning. A 100 μl reaction mixture was prepared, containing 500 ng of DNA, 500 ng of 3′ and 5′ primers, 16 nM dNTP, 10 mM Tris-HCl (pH 8,3), 50 mM KCl, 1.5 mM MgCl₂ and 2 U of AmpliTaq DNA polymerase (Perkin-Elmer, Roissy, France), then subjected to 30 cycles of amplification [30 s at 94° C., 30 s at 61° C., 30 s at 72° C.] using a GenAmp PCR System 9600 (Perkin-Elmer).

PCR products were analyzed by electrophoresis on a 2% agarose gel. The amplified products of 770 bp for Anti-GPA scFv and 340 bp for C4BPβ were purified by QIAquick PCR Purification Kit protocol (Qiagen, Hilden, Germany) and ligated in pEFIRES-P vector. The ligation product was introduced into Escherichia coli and one positive clone was sequenced (Genomexpress, Meylan, France).

2.4 Cloning of the Anti-CEA VHH-C4BPα Construct

DNA of anti-CEA VHH was kindly provided by D. Baty (CNRS, UPR9027, Laboratoire des Systemes Macromoléculaires, Marseille, France).

The VHH DNA fragment was amplified using forward primer 5′-CGCGAGAGATCTGAGGTGCAGCTGGTGGAG-3′ (SEQ ID NO:18) (Eurogentec, Angers, France) and reverse primer 5′-CGCGAGTCCGGATGAGGAGACAGTGACCTG-3′ (SEQ ID NO:19) (Eurogentec, Angers, France). DNA of anti-CEA VHH was used for PCR amplification. A 100 μl reaction mixture was prepared, containing 500 ng of DNA, 500 ng of 3′ and 5′ primers, 16 nM dNTP, 10 mM Tris-HCl (pH 8,3), 50 mM KCl 1.5 mM MgCl₂ and 2 U of AmpliTaq DNA polymerase (Perkin-Elmer, Roissy, France), then subjected to 30 cycles of amplification [30 s at 94° C., 45 s at 64° C., 1 min at 72° C.] using a GenAmp PCR System 9600 (Perkin-Elmer). PCR products were analyzed by electrophoresis on a 2% agarose gel.

The restriction sites BglII and BspEI (underlined sequences) were inserted into forward and reverse primers respectively to facilitate anti-CEA VHH insert in pEFIRES-P vector. Conditions for PCR amplification of C4BPα were previously described. The amplified products of 360 bp for anti-CEA VHH and 225 bp for C4BPα were by QIAquick PCR Purification Kit protocol (Qiagen, Hilden, Germany) and ligated in pEFIRES-P vector. The ligation product was introduced into Escherichia coli and one positive clone was sequenced (Genomexpress, Meylan, France).

2.5 293T Cell Culture and Transfection

Human embryonic kidney cells, 293T (ATCC CRL-11268) were routinely maintained in Dulbecco's modified Eagle Medium with glucose 4500 mg/l, L-glutamine 580 mg/l and sodium pyruvate 110 mg/l (Gibco, Grand Island, USA) supplemented with 10% heat-inactivated fetal calf serum and penicillin/streptomycin/fungizone (1000 U/ml; 1000 μg/ml; 2.5 μg/ml). Cells were grown at 37° C. in a humidified atmosphere of 5% CO₂.

Three million and half cells were transfected in a 25 cm² flask with 10 μg of DNA by 20 μl of lipofectamine 2000 (Invitrogen, Carlsbad, USA). Transfected cells were plated in the same medium supplemented with 20 μg/ml puromycin (Sigma, St Louis, USA) to select resistant clones.

Homomultimeric TTFgC-C4BPα, anti-GPA scFv-C4BPα or anti-CEA VHH-C4BPα and Heteromultimeric TTFgC-C4BPα/anti-GPA scFv-C4BPα or TTFgC-C4BPα/anti-CEA VHH-C4BPα secreting clones were screened after limiting dilution by western blotting under reducing conditions.

3 DNA Constructions for SF9 Cell Transfections and Infections

3.1 Cloning of the Anti-GPA scFv—C4BPα and TTFgC-C4BPα Constructs

cDNA of anti-GPA-scFv was amplified by PCR using forward primer 5′-CGCGAGCCCGGGGCAGGTGAAACTGCAGCAGTCT-3′ (SEQ ID NO:20) (Eurogentec, Angers, France) and reverse primer 5′-CGCGAGGCGGCCGCCCGTTTTATTTCAGCTTGGT-3′ (SEQ ID NO:21) (Eurogentec, Angers, France). The restriction sites XmaI and NotI (underlined sequences) were inserted into forward and reverse primers respectively to facilitate anti-GPA scFv subcloning.

PCR amplification of C4BP was fulfilled by forward primer: 5′-CGCGAGGCGGCCGCATCCGGAGGCGGTGGCTCG-3′ (SEQ ID NO:22) (Eurogentec, Angers, France) and reverse primer: 5′-CGCGAGAGATCTTATTACAACAATTTTGCCTTC-3′ (SEQ ID NO:23) (Eurogentec, Angers, France). Restriction sites NotI and BgIII (underlined sequences) were inserted into forward and reverse primers respectively to facilitate C4BPα subcloning. A 100 μl reaction mixture was prepared, containing 500 ng of DNA, 500 ng of 3′ and 5′ primers, 16 nM dNTP, 10 mM Tris-HCl (pH 8,3), 50 mM KCl, 1.5 mM MgCl₂ and 2 U of AmpliTaq DNA polymerase (Perkin-Elmer, Roissy, France), then subjected to 30 cycles of amplification [30 s at 94° C., 30 s at ° C., 30 s at 72° C.] using a GenAmp PCR System 9600 (Perkin-Elmer). The amplified cDNA of C4BPα product was purified and ligated in pAcGP67C baculovirus transfer vector (PharMingen, San Diego, USA).

The TTFgC-C4BPα DNA was amplified using forward primer 5′-CGCGAGCCCGGGGCTGGATTGTTGGGTTGATAATG-3′ (SEQ ID NO:24) (Eurogentec, Angers, France) with restriction site (underlined sequence) of XmaI, and the same reverse primer as anti-GPA scFv-C4BPα. The amplified product was ligated in pAcGP67C baculovirus transfer vector. The ligation product was introduced into Escherichia coli and one clone was sequenced (Genomexpress, Meylan, France) (FIG. 3, and SEQ ID NO: 5 and NO:6; FIG. 4, SEQ ID NO:7 and NO:8).

3.2 SF9 Cell Culture and Infection

Sf9 cells were cotransfected with viral DNA BaculoGold linearized Baculovirus DNA (Becton Dickinson, Pont de Claix, France) and anti-GPA scFv-C4BPα or TTFgC-C4BPα constructs. All recombinant viruses were isolated from the transfection supernatant through plaque purification and virus stocks were generated by propagating viruses in Sf9 cells and titrated using end-point dilution assays according to the Baculovirus Expression Vector Systems and Insect Cell Culture Techniques Guide (Invitrogen, Cergy Pontoise, France). The presence of the different inserts was verified by PCR.

4 Detection of the Homo and Heteromultimeric Produced Molecules 4.1 Western Blotting Detection

TTFgC-C4BPα, anti-GPA scFv-C4BPα or anti-CEA VHH-C4BPα transfected cell supernatants were concentrated 5 fold by using centricon 100 (Millipore, Bedford, USA). Proteins were separated in sodium dodecyl sulfate (SDS)-polyacrylamide gel under reducing conditions and transferred into nitro-cellulose membrane. The presence of the TTFgC-C4BPα (His₆) monomers and anti-CEA VHH-C4BPα (His₆) were visualised by using a mouse anti-His₆ peroxydase antibody (Roche, Indianapolis, USA) used at one unit in PBS (Biomérieux, Marcy I'Étoile, France). Anti-GPA scFv-C4BPα was detected by using a rabbit anti scFv antibody (kindly provided by Dr J. L Teillaud, Unite INSERM U 255, Paris) at 10 μg in 0.1% Tween 20 and 1% milk, PBS.

Heteromultimeric TTFgC-C4BPα/anti-GPA scFv-C4BPα under reducing conditions as previously described.

4.2 Biosynthetic Cell Labelling and Immunoprecipitation

Cells were cultured for 1 night, in RPMI 1640 without cysteine and methionine (Sigma, St Louis, USA) supplemented with 10% heat-inactivated FCS, glutamine (2 mM), penicillin/streptomycin/fungizone (1000 U/ml; 1000 μg/ml; 2.5 μg/ml), and 50 μCi of [³⁵S]methionine cysteine (Amersham Biosciences, Buckinghamshire, England). Twenty five microliters of goat anti-mouse IgG-coated magnetic beads (Dynal, Oslo, Norway) were washed three times with 0.1% BSA PBS (Sigma, St Louis, USA) then incubated with 1 μg of anti-tetanus toxin fragment C (Roche, Indianapolis, USA) for 1 night at 4° C. Beads were washed three times with 0.1% BSA PBS. Transfected cell culture supernatants were incubated with beads for 1 night at 4° C. Washed beads were then resuspended in SDS-PAGE sample buffer for electrophoresis. Reduced and unreduced immunoprecipitates were subjected to electrophoresis in a 5% SDS acrylamide gel.

5 Analysis of the Heteromultimeric Molecule Activity 5.1 Assessment of the Fixation of Heteromultimeric Proteins

5.1.1 Fixation of TTFgC-C4BPα/anti-GPA scFv-C4BPα on Erythrocytes

a. Direct Hemagglutination

Sepharose columns were purchased from DiaMed (Paris, France). Twenty microliters of a 2.5% suspension of E were incubated for 45 minutes at 37° C. with 50 μl of supernatant of transfected cells. Agglutination was then assessed in columns after a 1,000 g centrifugation for 10 minutes at room temperature.

b. Flow Cytometry Assay

TTFgC-C4BPα/anti-GPA scFv-C4BPα binding on erythrocytes was analysed by flow cytometry. Washed E were incubated for 1 hour at room temperature with transfected cells supernatant then washed three times with 1% BSA PBS. Human serum or 1 μg of anti-tetanus toxin fragment C (Roche, Indianapolis, USA) were added for 45 minutes at room temperature. Erythrocytes were washed twice, and then 1 μg of goat anti-Human Ig (H+L) biotinylated antibody (Southern Biotechnology Associates, Birmingham, USA) or anti-mouse Ig biotinylated antibody (Amersham Biosciences, Buckinghamshire, UK) were added before 1.5 μg of Streptavidin R-Phycoerythrin conjugated antibody (tebu-bio, Burlingame,USA) conjugated detection system.

Flow cytometry of stained cells was performed on a FACStarPlus apparatus (Becton Dickinson, Mountain View, Calif., USA). At least 10,000 events for each sample were collected. Mean fluorescence channel was used to quantify the staining of each sample.

TTFgC-C4BPα/anti-GPA scFv-C4BPα distribution pattern was analyzed using fluorescence microscopy.

5.1.2 Fixation of TTFgC-C4BPα/anti-CEA VHH-C4BPα on LS174T Cells Assessed by Flow Cytometry

TTFgC-C4BPα/anti-CEA VHH-C4BPα binding to LS174T cells (ATCC CCL 188) was analysed by flow cytometry. Washed LS174T cells were incubated with transfected cell supernatant for 90 minutes at 4° C. then washed three times with 0.5% BSA PBS. 1 μg of anti-tetanus toxin fragment C or 3.3 μg monoclonal anti-c-myc (mouse IgG1 isotype) (Sigma, Saint Louis, USA) for monomeric c-myc tagged anti-CEA VHH provided by Dr. Baty, were added for 45 minutes at room temperature as positive control.

LS174T cells were washed twice, and then anti-mouse Ig biotinylated antibody (Amersham Biosciences, Buckinghamshire, England) was added before R-Phycoerythrin conjugated Streptavidin detection system.

5.2 Complement (C) Fixation Tests

5.2.1 Assessment of C Activation by TTFgC-C4BPα/Anti-GPA scFv-C4BPα using Hemolytic Assay

Fifteen microliters of 2.5% suspension of E were incubated with 200 μl of 5 fold concentrated transfected cell supernatant at room temperature for 1 hour in 0.24 M glycin, 3 mM sodium phosphate (pH 6.8), 31 mM NaCl, low ionic strength saline buffer including 0.15 mM Ca²⁺, and 0.5 mM Mg²⁺.

After 5 minutes of 160 g centrifugation at room temperature, supernatant was removed and 100 μl of serum of a healthy individual who gave an informed consent for research used, recently vaccinated against tetanus were then added (E were also from the same person). Monoclonal antibody (MoAb) against glycophorin A (R18) was used as positive control. After 1 hour incubation at 37° C. and a quick cooling in an ice-water bath, tubes were centrifuged for 10 minutes at 160 g, then the 630-405 nm optical density of the supernatants was determined using a microplate reader (SLT, Labinstruments, Vietech, St Bonnet De Mure, France).

5.2.2 Assessment of C Activation by TTFgC-C4BPα/Anti-GPA scFv-C4BPα using Flow Cytometry Analysis

Fifteen microliters of 2.5% suspension E (O Rh(D)-negative) was added to 100 μl of transfected cell supernatant for 1 hour at room temperature. After centrifugation as previously described, supernatant is removed and 100 μl of heat inactivated serum of recently vaccinated person against tetanus were added. Incubation at room temperature for 1 hour was followed by 2 times washing with 1% BSA PBS. Fifty microliters of Human C5-deficient serum, two fold diluted in low ionic strength saline buffer including 0.15 mM Ca²⁺ and 0.5 mM Mg²⁺ was added, and the mixture was incubated for 1 hour at 37° C. Human C3b deposits were revealed by fluorescein-labeled goat antiserum against human C3b (Immunotech, Marseille, France) and C4d by a biotinylated monoclonal anti-Human C4d (Quidel, San Diego, USA) followed by Streptavidin R-Phycoerythrin conjugated detection system. E were washed twice, stabilized in 0.37% formaldehyde PBS buffer, and then analyzed on a FACStar Plus (Becton Dickinson).

C4d and C3b distribution pattern were analyzed using fluorescence microscopy.

Results

The results obtained with the Baculovirus expression system were similar to those of the 293T expression system.

1 Detection of Homo and Heteromultimeric Recombinant Proteins Secreted

The production of homomultimeric and heteromultimeric recombinant proteins was characterized by Western blotting and radioactive labeling.

1.1 Homomultimeric Molecules 1.1.1 TTFgC-C4BPα Protein

TTFgC-C4BPα monomers were identified by using an anti-His immunoblotting detection. GFP-(His)₆ was used as positive control; Its molecular weight was 32 Kda. The apparent molecular weight of TTFgC-C4BPα monomers was assessed from SDS-PAGE under reducing conditions and was found to be 82 Kda.

Multivalent TTFgC recombinant proteins were obtained using C4BPα multimerizing fragments fused at the C-terminal end of the molecule. They were soluble and stable in culture supernatant of the selected clones.

³⁵S amino-acid labeling experiments showed that two molecular species of more than 500 KDa apparent molecular weight on SDS-PAGE analysis were secreted. This pattern is compatible with a 6 and 7 valence multimers, a counterpart of the physiological pattern of C4BPα multimers that consists mainly of octamers (656 KDa) together with a few heptamers (574 KDa) and hexamers (492 KDa).

1.1.2 Anti-GPA scFv-C4BPα Protein

A single molecular species of anti-GPA scFv-C4BPα protein with an apparent molecular weight more than 210 KDa was detected by SDS-PAGE analysis in native conditions. This multimer was an heptamer (245 KDa). In reducing conditions, the apparent molecular weight of the monomer was 35 Kda.

Anti-CEA VHH-C4BPα Protein

Anti-CEA VHH-C4BPα monomers were identified by using an anti-His immunoblotting detection. The apparent molecular weight was assessed from SDS-PAGE under reducing conditions and was found to be 22 Kda.

1.2 Heteromultimeric Molecules

1.2.1 TTFgC-C4BPα/Anti-GPA scFv-C4BPα Recombinant Proteins

Under reducing conditions, TTFgC-C4BPα and anti-GPA scFv-C4BPα monomers were identified using anti-His immunoblotting detection. Their molecular weights were found to be 82 KDa and 35 KDa respectively.

Heteromultimeric TTFgC-C4BPα/anti-GPA scFv-C4BPα recombinant protein were detected by radioactive labeling in nonreducing conditions. After five days of exposure several valences of TTFgC-C4BPα/anti-GPA scFv-C4BPα with an apparent molecular weight of more than 300 KDa can be visualized. Two main valences were detected with 2 hours of exposure. Multivalent TTFgC recombinant proteins were used as positive control.

1.2.2 TTFgC-C4BPα/Anti-CEA VHH-C4BPα Recombinant Proteins

TTFgC-C4BPα and anti-CEA VHH-C4BPα monomers were identified using anti-H is immunoblotting detection under reducing conditions; their molecular weights were found to be 82 KDa and 22 KDa respectively.

Heteromultimeric TTFgC-C4BPα/anti-CEA VHH-C4BPα molecules were detected by radioactive labeling in nonreducing conditions and showed three main valences with apparent molecular weight of more than 400 KDa. Multivalent TTFgC recombinant proteins and heteromultimeric TTFgC-C4BPα/anti-GPA scFv-C4BPα recombinant molecules were used as positive control.

2 Analysis of Heteromultimeric Molecule Activity 2.1 Analysis of the Fixation of Heteromultimeric Molecules to the Cell Membrane Surface

2.1.1 Analysis of the Fixation of TTFgC-C4BPα/Anti-GPA scFv —C4BPα and TTFgC-C4BPα/Anti-GPA scFv —C4BPβ Molecule at the E Membrane Surface

a. Direct Hemagglutination

Anti-GPA ScFv-C4BPα and TTFgC-C4BPα/anti-GPA ScFv-C4BPα directly agglutinated erythrocytes as R18 natif antibody (FIG. 5).

Supernatants are still functional by direct hemagglutination after 6 months at 4° C., this proved stability of these recombinant heteromultimers.

b. Flow Cytometry

To demonstrate the TTFgC-C4BPα/anti-GPA scFv-C4BPα and TTFgC-C4BPα/anti-GPA scFv-C4BPβ specific binding at the erythrocyte membrane surface quantitative flow cytometry analysis with supernatants of transfected 293T cells were performed.

Multimeric TTFgC-C4BPα/anti-GPA scFv-C4BPα (FIG. 6.f) as well as TTFgC-C4BPα/anti-GPA scFv-C4BPβ molecule (FIG. 6.d; FIG. 6.e) were able to bind at the erythrocyte membrane surface.

Homomultimeric TTFgC-C4BPα and homomultimeric anti-GPA scFv-C4BPα were used as negative controls:

-   -   homomultimeric TTFgC-C4BPα was not able to bind at the E (FIG.         6.a).     -   homomultimeric anti-GPA scFv-C4BPα was attached to E but not         detected by flow cytometry as not revealed by anti-TTFgC (FIG.         6.b).

c Fluorescence Microscopy

The distribution of heteromultimers to the E membrane surface was analyzed by using fluorescence microscopy and was homogeneous (FIG. 3).

2.1.2 Analysis of TTFgC-C4BPα/Anti-CEA VHH-C4BPα Molecule Binding at the LS174T Cell Membrane Surface

a Flow Cytometry

To demonstrate the TTFgC-C4BPα/anti-CEA VHH-C4BPα specific binding at the LS174T membrane surface; quantitative flow cytometry analysis with supernatants of transfected 293T cells were performed.

Monomeric anti-CEA VHH-c-myc and TTFgC-C4BPα/anti-CEA VHH-C4BPα heteromultimeric molecules were detected at the LS174T membrane surface (FIG. 8.d and 8.c).

Homomultimeric VHH-C4BPα molecules were attached to the LS174T cells surface but not detected by flow cytometry because not revealed by anti-TTFgC (FIG. 8.b).

b Fluorescence Microscopy

The distribution of heteromultimeric TTFgC-C4BPα/anti-CEA VHH-C4BPα to the LS174T membrane surface was analyzed using fluorescence microscopy and was heterogeneous (FIG. 9).

2.2 Analysis of Complement Activation by TTFgC-C4BPα/Anti-GPA scFv-C4BPα Molecules

The ability of heteromultimeric TTFgC-C4BPα/anti-GPA scFv-C4BPα molecules to activate the complement was tested.

Erythrocytes were incubated with a C5-deficient serum in presence of TTFgC-C4BPα/anti-GPA scFv-C4BPα constructs transfected 293T cell supernatant. The C5-deficiency of this serum stops the complement cascade and E are not lysed. C4d binding was detected at the erythrocyte membrane surface by flow cytometry and fluorescence microscopy (FIG. 10 and FIG. 11B) as well as C3b (Data not shown and FIG. 11A). Erythrocytes from an healthy individual, recently vaccinated against tetanus were incubated with his serum, in presence of TTFgC-C4BPα/anti-GPA scFv-C4BPα transfected cell supernatant. Anti-tetanus toxin antibodies present in the serum are able to link to the TTFgC portion of the TTFgC-C4BPα/anti-GPA scFv-C4BPα heteromultimeric molecules attached at the erythrocyte surface. Erythrocytes have been opsonized and complement activation cascade started. Under these conditions the final membrane attack pathway of complement could be activated and lysed the erythrocytes.

FIG. 12 showed that heteromultimeric molecules induce the erythrocyte lysis at 87% whereas homomultimeric molecules are not able to induce erythrocyte lysis at all. 

1. A protein construct, comprising (i) a targeting moiety that is capable of binding to a target cell, and (ii) an effector immunogenic moiety that is capable of triggering an existing, vaccine-induced or natural, immune response.
 2. The protein construct of claim 1, that is in monomeric form, such as a monomeric fusion protein.
 3. The protein construct of claim 1, that is in multimeric form.
 4. The multimeric protein construct of claim 3, that comprising a multimerizing scaffold bearing (i) at least one targeting moiety that is capable of binding to a target cell, and (ii) at least two, preferably at least five, effector immunogenic moieties that are capable of triggering an existing, vaccine-induced or natural, immune response.
 5. The protein construct of claim 4, wherein the scaffold is a C4BP protein, or comprises a multimerizing fragment thereof.
 6. The protein construct of claim 5, wherein the scaffold comprises the C-terminal part of the alpha chain of C4BP and/or of the beta chain of C4BP.
 7. The protein construct according to claim 1, wherein the targeting moiety is selected from the group consisting of an antibody, a binding fragment thereof, a ligand to a target cell receptor, and a lectin.
 8. The protein construct according to claim 7, wherein the targeting moiety is an antibody, or a binding fragment thereof, against a tumor associated antigen.
 9. The protein construct according to claim 7, wherein the targeting moiety is an antibody, or a binding fragment thereof, against a Rhesus antigen.
 10. The protein construct according to claim 1, wherein the effector moiety is a vaccine antigen.
 11. The protein construct of claim 10, wherein the effector moiety is a toxin fragment that is immunogenic but non-toxic.
 12. The protein construct of claim 10, wherein the effector moiety is fragment C of tetanus toxin (TTFgC).
 13. The protein construct according to claim 1, wherein the effector moiety is a self-antigen against which natural antibodies exist.
 14. The protein construct of claim 13, wherein the effector moiety is actin or tubulin, or an antigenic fragment thereof.
 15. An isolated nucleic acid that encodes a fusion protein of claim
 2. 16. A method for preparing a heteromultimeric protein construct of claim 4, which method comprises a) transfecting host cells with a nucleic acid vector that encodes the targeting moiety fused to a first scaffold polypeptide, and with a nucleic acid vector that encodes the effector moiety fused to a second scaffold polypeptide, wherein said second scaffold polypeptide is capable of multimerization with said first scaffold polypeptide, b) expressing the expression products and allowing them to multimerize; c) recovering the heteromultimeric protein constructs thus produced.
 17. The method of claim 16, wherein the host cells are co-transfected with said two nucleic acid vectors.
 18. The method of claim 16, comprising a1) transfecting a host cell with a nucleic acid vector that encodes the targeting moiety fused to a first scaffold polypeptide, under conditions allowing expression of said targeting moiety fused to said scaffold polypeptide; a2) transfecting another host cell with a nucleic acid vector that encodes the effector moiety fused to a second scaffold polypeptide, under conditions allowing expression of said targeting moiety fused to said scaffold polypeptide, wherein said second scaffold polypeptide is capable of multimerization with said first scaffold polypeptide, b) recovering the expression products and contacting them under conditions that allow them to multimerize.
 19. A pharmaceutical composition comprising a protein construct of claim 1, in association with a pharmaceutically acceptable carrier.
 20. A pharmaceutical composition comprising a nucleic acid of claim 15, in association with a pharmaceutically acceptable carrier.
 21. Use of a protein construct of claim 1, for the preparation of a medicament intended for redirecting an immune response that was pre-existing in a patient, toward an undesired target cell.
 22. The use of claim 21, wherein the target cell is a tumor cell.
 23. The use of claim 21, wherein the target cell is an erythrocyte.
 24. The use of claim 19, wherein the protein construct is a heteromultimeric protein comprising fragment C of tetanus toxin as an effector moiety, and the patient is naturally vaccinated against tetanus, or was previously subjected to a vaccination against tetanus.
 25. Use of a nucleic acid of claim 15, for the preparation of a medicament intended for redirecting an immune response that was pre-existing in a patient, toward an undesired target cell. 